Hi All, Master recycler and borderline hoarder John Fischer here with KLCC's Living Less Unsustainably.
I don't throw much away. Partly because our family buys in bulk, re-uses bags, and wears clothes until they are worn out - really worn out. But also because I keep things that might be useful - just in case. Some things are obvious.
Any piece of two-by lumber - two-by-four, two-by-six,... at least 14.5 inches long can be used as blocking on a construction job - by me, family, or friends. Or they can become firewood. Any cedar - from an old fence or deck gets set aside to turn into tomato stakes, garden edging, bean trellises, or firewood. Construction screws can be used over and over - especially star or square drive. Putting things together with screws means taking them apart is easy, and the leftover screws are ready for the next project - with the salvaged wood we just talked about. If you're using salvaged wood - wear gloves. There's nothing pointier than an old-growth splinter.

Paint thinner can be used for cleaning brushes again and again. While oil based paints are getting less common, they have applications where they work best. If you use three small half cup doses of paint thinner to clean the brush, then pour the leftovers into a glass jar, the pigments will settle to the bottom, and the clear thinner on top can be used again - and again.
There are some things I don't save. That old fridge, or washer and dryer get donated to St, Vinnies now, and I buy them back later when I need them.
When in doubt throw it out is fine when you are confused about recycling, but if somebody may need it, and our local re-use stores - BRING and Habitat - don't want it, if you have the space, store it and pass it on. Your friends - and the Earth will thank you.
I'm John Fischer with Living Less unsustainably.